Multiport power electronics circuitry for integration of renewable energy sources in low power applications : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering at Massey University, Palmerston North, New Zealand

The increasing demand for electricity and the global concern about environment has led energy planners and developers to explore and develop clean energy sources. Under such circumstances, renewable energy sources (RES) have emerged as an alternative source of energy generation. Immense development has been made in renewable energy fields and methods to harvest it. To replace conventional generation system, these renewable energy sources must be sustainable, reliable, stable, and efficient. But these sources have their own distinguished characteristics. Due to sporadic nature of renewable energy sources, the uninterrupted power availability cannot be guaranteed. Handling and integration of such diversified power sources is not a trivial process. It requires high degree of efficiency in power extraction, transformation, and utilization. These objectives can only be achieved with the use of highly efficient, reliable, secure and cost-effective power electronics interface. Power electronics devices have made tremendous developments in the recent past. Numerous single and multi-port converter topologies have been developed for processing and delivering the renewable energy. Various multiport converter topologies have been presented to integrate RES, however some limitations have been identified in these topologies in terms of efficiency, reliability, component count and size. Therefore, further research is required to develop a multiport interface and to address the highlighted issues. In this work, a multi-port power electronics circuitry for integration of multiple renewable energy sources is developed. The proposed circuitry assimilates different renewable sources to power up the load with different voltage levels while maintaining high power transfer efficiency and reliability with a simple and reliable control scheme. This research work presents a new multiport non-isolated DC-DC buck converter. The new topology accommodates two different energy sources at the input to power up a variable load. The power sources can be employed independently and concurrently. The converter also has a bidirectional port which houses a storage device like battery to store the surplus energy under light load conditions and can serve as an input source in case of absence of energy sources. The new presented circuitry is analytically examined to validate its effectiveness for multiport interface. System parameters are defined and the design of different components used, is presented. After successful mathematical interpretation, a simulation platform is developed in MATLAB/Simscape to conduct simulations studies to verify analytical results and to carry out stability analysis. In the final stage, a low power, low voltage prototype model is developed to authenticate the results obtained in simulation studies. The converter is tested under different operating modes and variable source and load conditions. The simulation and experimental results are compiled in terms of converter’s efficiency, reliability, stability. The results are presented to prove the presented topology as a highly reliable, stable and efficient multiport interface, with small size and minimum number of components, for integration of renewable energy sources

Building Energy Load Forecasting using Deep Neural Networks

Ensuring sustainability demands more efficient energy management with minimized energy wastage. Therefore, the power grid of the future should provide an unprecedented level of flexibility in energy management. To that end, intelligent decision making requires accurate predictions of future energy demand/load, both at aggregate and individual site level. Thus, energy load forecasting have received increased attention in the recent past, however has proven to be a difficult problem. This paper presents a novel energy load forecasting methodology based on Deep Neural Networks, specifically Long Short Term Memory (LSTM) algorithms. The presented work investigates two variants of the LSTM: 1) standard LSTM and 2) LSTM-based Sequence to Sequence (S2S) architecture. Both methods were implemented on a benchmark data set of electricity consumption data from one residential customer. Both architectures where trained and tested on one hour and one-minute time-step resolution datasets. Experimental results showed that the standard LSTM failed at one-minute resolution data while performing well in one-hour resolution data. It was shown that S2S architecture performed well on both datasets. Further, it was shown that the presented methods produced comparable results with the other deep learning methods for energy forecasting in literature

A review of PHIL testing for smart grids—selection guide, classification and online database analysis

The Smart Grid is one of the most important solutions to boost electricity sharing from renewable energy sources. Its implementation adds new functionalities to power systems, which increases the electric grid complexity. To ensure grid stability and security, systems need flexible methods in order to be tested in a safe and economical way. A promising test technique is Power Hardware In-the-Loop (PHIL), which combines the flexibility of Hardware-In-the-Loop (HIL) technique with power exchange. However, the acquisition of PHIL components usually represents a great expense for laboratories and, therefore, the setting up of the experiment involves making hard decisions. This paper provides a complete guideline and useful new tools for laboratories in order to set PHIL facilities up efficiently. First, a PHIL system selection guide is presented, which describes the selection process steps and the main system characteristics needed to perform a PHIL test. Furthermore, a classification proposal containing the desirable information to be obtained from a PHIL test paper for reproducibility purposes is given. Finally, this classification was used to develop a PHIL test online database, which was analysed, and the main gathered information with some use cases and conclusions are shown

Stator Current Analysis by Subspace Methods for Fault Detection in Induction Machines

International audienceThis paper aims to develop a condition monitoring architecture for induction machines, with focus on bearing faults. The main objective of this paper is to identify fault signatures at an early stage by using high-resolution frequency estimation techniques. In particular, we present two subspace methods, which are Root-MUSIC and ESPRIT. Once the frequencies are determined, the amplitude estimation is obtained by using the Least Squares Estimator (LSE). Finally, the amplitude estimation is used to derive a fault severity criterion. The experimental results show that the proposed architecture has the ability to measure the faults severity

Neighboring-Pixel-Based Maximum Power Point Tracking Algorithm for Partially Shaded Photovoltaic (PV) Systems

In this paper, a neighboring-pixel-based virtual imaging (NPBVI) technique is developed to comprehensively detect the shading conditions on PV arrays. The proposed VI technique is then merged with a probabilistic mechanism of shaded module currents. Finally, a mathematical model is presented, which predicts the current voltage (I-V) region corresponding to the global maximum (GM) of the shaded PV array. The effectiveness of the proposed NPBVI MPPT is validated through numerous experiments that were carried out using a hardware prototype with a 150 W power rating. For the experiments, a PV array consisting of 3 × 2 (Np× Ns ) 20 W PV modules was utilized. The experiments showcase agreement that the proposed method successfully identified the GM region of a partially shaded PV array

Quantitative comparison of permanent magnet linear machines for ropeless elevator

Paper no. YD-026263This paper presents a quantitative comparison of three topologies of double-sided long-stator type permanent magnet linear machines (PMLMs) as possible candidates for the ropeless elevator propulsion system. First, the parameters of each PMLM topology are designed using the same criteria. Then the finite element method (FEM) is employed to evaluate the performance of each topology. Specifically, the translator mass, propulsion forces, detent forces, and no-load EMFs are analyzed and compared. The quantitative comparison results show that the Halbach array PMLM configuration is preferable for the ropeless elevator application because of its small detent force as well as low total mass. © 2015 IEEE.postprin

Control strategies and applications of three-phase direct matrix converters

University of Technology Sydney. Faculty of Engineering and Information Technology.AC-to-AC converters have been widely used in various areas in the real world. In industrial applications, the AC-to-AC power conversion is usually accomplished by indirect converters. In these traditional converters, AC power is firstly converted into DC power by a rectifier, and then the DC power is converted into AC power by an inverter. The rectifier and inverter are usually connected via an intermediate bulky DC-link capacitor. The use of the DC-link capacitor in these converters makes the equipment volume bulky, reduces the lifetime, increases the design complexity and decreases the system efficiency. Therefore, it is of great benefit to remove the bulky DC-link capacitor or propose new converter topologies. A matrix converter (MC) does not require large energy storage elements and it has emerged as a potential solution to AC-to-AC conversion. A three-phase direct MC comprises nine bidirectional semiconductor switches arranged in a 3×3 matrix form to realize the direct AC-to-AC conversion. Thanks to benefits such as bidirectional power flow, compact volume, controllable input power factor and sinusoidal waveform, MCs have attracted research interests and plenty of projects on MC have been reported. MC is also regarded as an all-silicon converter. However, there are some drawbacks associated with MCs and they have very limited industrial applications. These drawbacks include low voltage transfer ratio (VTR), sensitivity to the grid variations and complex modulation. Some MC application areas need more exploration. The work in this thesis is carried out to contribute to possible solutions to some of the above issues by investigating some control strategies and applications of MCs. The main contributions included in this work are summarized as follows: (1) A simple decoupling controller is designed for the MC-based unified power flow controller (UPFC) (MC-UPFC) to regulate the power flow in a transmission system. The controllable regions of the MC-UPFC are also analyzed. A design procedure for the closed-loop controller in the MC-UPFC is presented. (2) A modified PI controller is proposed for the improvement of the steady-state performance by including a current feedforward path. More control flexibility is provided because of the feedforward controller. A PR controller is designed for the MC and this has good performance. (3) A hysteresis current controller is proposed for the MC to drive AC motors. Both fixed-band and sinusoidal-band hysteresis controllers are investigated, and their performance is compared. The hysteresis controller is a very simple and practical controller for the MC. For the MC-based motor drive, a direct torque control (DTC) technique is also investigated. (4) Model predictive control (MPC) is investigated to control the MC. This scheme is used in an MC-based microgrid. In the islanded mode, predictive voltage control is employed to regulate the MC output voltages to supply various loads. An improved VTR is observed. When the microgrid is connected to the utility grid, power flow is the main objective. The performance of the controller is tested under various conditions including input disturbance and different loads. (5) An MC prototype is built to support the research. The prototype hardware includes main circuit, drives, supplies, analog to digital conversion (ADC) conditioning circuits, and sensor board. The algorithm is implemented in Matlab Simulink with C2000 hardware support packages for TI DSP processors. Various experimental tests are carried out to support the proposed strategies

Complex-conjugate control of a linear magnetic-geared permanent-magnet machine for Archimedes wave swing based power generation

Paper no. YF-005177This paper deals with control of a linear magnetic-geared permanent-magnet machine for Archimedes wave swing based wave power generation using maximum power point tracking (MPPT). Firstly, the linear magnetic-geared permanent-magnet generator structure is presented. The machine modeling is established based on finite element analysis (FEA). Secondly, by analyzing the dynamic model of wave power, the MPPT algorithm for direct-drive wave power generation is developed. Then, the performance for maximizing wave power absorption is verified and evaluated by the circuit simulator. The results verify that the MPPT algorithm is valid for the direct-drive wave power generation. © 2015 IEEE.postprin

Electromagnetic design of a new hybrid-excited flux-switching machine for fault-tolerant operations

Paper no. YD-011541In this paper, a new hybrid-excited flux-switching (HEFS) machine is proposed with the outer-rotor configuration, which possesses the distinct feature of fault-tolerant operation. Comparing with the conventional permanent-magnet (PM) machine, it combines merits of flux control, high mechanical integrity, and low-cost. Furthermore, its fault-tolerant feature ensures its continuous operation in the event of winding faults. Hence, a new 12/10-pole HEFS machine is designed and implemented in this paper. By using time-stepping finite element method, open circuit (OC) fault and short circuit (SC) faults on the armature winding are investigated in the proposed machine for the fault-tolerant operation. The phase-current reconfiguration and flux control are applied for the remediation of the OC fault, while the SC faults is remedied by the phase-current reconfiguration merely. Both approaches demonstrate their good performances for the fault-tolerant operation. © 2015 IEEE.postprin

Comparison of Optimized Control Strategies of a High-Speed Traction Machine with Five Phases and Bi-Harmonic Electromotive Force

The purpose of the paper is to present the potentialities in terms of the control of a new kind of PM synchronous machine. With five phases and electromotive forces whose first (E1) and third (E3) harmonics are of similar amplitude, the studied machine, so-called bi-harmonic, has properties that are interesting for traction machine payload. With three-phase machines, supplied by a mono-harmonic sinusoidal current, the weak number of freedom degrees limits the strategy of control for traction machines especially when voltage saturation occurs at high speeds. As the torque is managed for three-phase machines by a current with only one harmonic, flux weakening is necessary to increase speed when the voltage limitation is reached. The studied five-phase machine, thanks to the increase in the number of freedom degrees for control, aims to alleviate this fact. In his paper, three optimized control strategies are compared in terms of efficiency and associated torque/speed characteristics. These strategies take into account numerous constraints either from the supply (with limited voltage) or from the machine (with limited current densities and maximum acceptable copper, iron and permanent magnet losses). The obtained results prove the wide potentialities of such a kind of five-phase bi-harmonic machine in terms of control under constraints. It is thus shown that the classical Maximum Torque Per Ampere (MTPA) strategy developed for the three-phase machine is clearly not satisfying on the whole range of speed because of the presence of iron losses whose values can no more be neglected at high speeds. Two other strategies have been then proposed to be able to manage the compromises, at high speeds, between the high values of torque and efficiency under the constraints of admissible total losses either in the rotor or in the stator